Sometime between the thirty-second year (Alma 62:39) and the thirty-fifth year (Alma 62:52), Moroni "yielded up the command of his armies into the hands of his son" Moronihah (Alma 62:43). Moroni himself had become chief captain "when he was only twenty and five years old" (Alma 43:17). Moroni assumed this position at least by the 18th year, but more probably by 12th year (see the commentary on Alma 43:17). If Moronihah was born when his father was twenty years of age, he would have been somewhere between 19-28 years of age when he became chief captain. While the age isn't certain, one can still assume with some certainty that both Moroni and Moronihah assumed leadership of the Nephite armies at a young age. One might wonder why such a thing might happen. [Alan C. Miner, Personal Notes]
According to John Tvedtnes, if Moroni and Moronihah were part of a warrior caste, then it may not be out of line to suggest that this caste descended from the ancient kings. Nephi was the one who had taken the rather special sword from Laban in Jerusalem and personally wielded the sword in defense of his people (see Jacob 1:10). In this, he appears to have been following the ancient Near Eastern practice of the king being commander of the army. King David's troubles began when he neglected to personally lead the army of Israel in battle (see 2 Samuel 11, est. v. 1). From Egyptian, Assyrian, and Babylonian records, we learn that kings typically accompanied their armies into the field. . . . In any event, the sword of Laban was evidently passed down and was kept with the plates and the breastplate to Mormon. It is interesting to note that Mormon was a "pure descendant" of Lehi and Nephi (3 Nephi 5:20; Mormon 1:5), not only did he possess kingship lineage, but this lineage additionally gave him military rights of leadership. Therefore, if we apply this reasoning to the Moroni and Moronihah, we might guess that Moroni might have been a descendant of Nephite kings (hence the royal seed). [John A. Tvedtnes, "Book of Mormon Tribal Affiliation and Military Castes," in Warfare in the Book of Mormon, F.A.R.M.S., pp. 318-322]
Alma 62:43 Moroni yielded up the command of his armies into the hands of his son, whose name was Moronihah (Major Nephite Leaders) [[Illustration]]: The Major Leaders During Nephite History. [Church Educational System, Book of Mormon Student Manual: Religion 121 and 122, 1989, p. 160]